It is very sad for future engineers going to electronics shop and being teased. The dealer tends to ask some basic questions that most of the young engineers could not answer... Among them is the type of capacitors. There are plenty material and types of capacitors, but which 1 suits your need? I had summarized some common ones below and I took the info from :- http://en.wikipedia.org/wiki/Capacitor
Paper
· Used in older devices
· High voltage performance
· Susceptible to water absorption
· Replaced by film capacitors
Plastics
· Offer better stability and aging performance
· Useful in timer circuits
· Limited to low operating temperatures and frequency
Ceramic
· Small, cheap and useful for high frequency applications
· Capacitance varies strongly with voltage
· Poor performance when aged
· Classified as:
· Class 1 dielectrics (predictable variation of capacitance with temperature)
· Class 2 dielectrics (can operate at higher voltage)
· Often used in:
· often used in resonators
Glass and mica
· Extremely reliable, stable and tolerant to high temperatures and voltages
· Expensive for mainstream applications
Electrolytic and supercapacitors
· Used to store small and larger amounts of energy
· Material: aluminum or tantalum
· Offer high capacitance
· Suffer from poor tolerances, high instability, gradual loss of capacitance when subjected to heat and high leakage current.
· Poor quality may leak electrolyte which is harmful to PCB
· Conductivity drops at low temperatures (increases equivalent series resistance)
· Widely used for power supply conditioning
· Poor high frequency characteristic (unsuitable for many applications)
· Will self-degrade if unused for around a year
· When full power is applied, may short circuit/damage capacitor and usually blowing a fuse or causing arcing in rectifier tubes.
Tantalum vs Aluminum
Tantalum offers better frequency and temperature characteristic but higher dielectric absorption and leakage than of Aluminum caps.
OS-CON
· Polymerized organic semiconductor solid-electrolyte
· Offers longer life at higher cost than standard electrolytic caps
Supercapacitors
· Offer extremely high capacitance (5kF)
· May replace rechargeable batteries
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